High
305 on Navien NCM 1130HH

Your boiler's internal computer is failing to communicate properly with the main burner unit during startup.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Engine connectivity test failed. This test lasts for at most one minute following the start of engine operation. Measured current must be greater than 100 mA for 10 seconds to pass the test.

From this model's manual
Verified against the Navien/Navien Ncm 1130hh installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

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All 77 fault codes on the NCM 1130HH

Seeing a different code? Every code this model can display, in one place.

96979899100102114116117118121122127157158164187253254257258259260261262263264265266267268269270271272273274275276277278280281282283284285286287288289290291292293294295296298299300301302303304306307308309310311319394395396397

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